JPS6345469B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a plasma etching method suitable for forming a tapered side wall of a thin film pattern in the formation of fine thin film patterns in semiconductor integrated circuits, etc. be.

(Prior Art) In recent years, semiconductor integrated circuit manufacturing technology has been progressing in the direction of further miniaturization, and dry etching is becoming widely used as a highly accurate processing technology for thin film patterns. The cross-sectional shape of the thin film pattern formed by this dry etching method often has a rectangular shape. For example, using a parallel plate plasma etching apparatus, 25 SCCM of CCl ₂ F ₂ is injected as an etching reaction gas, the vacuum degree of the reaction chamber is maintained at 0.1 Torr, and a high frequency power of 400 W (13.56 MHz) is applied to remove polycrystalline crystals. When a silicon film is etched, the sidewalls of the etched polycrystalline silicon film are vertical. Since the side walls of such a thin film pattern having a rectangular cross-sectional shape have sharp steps, when a metal wiring or the like is deposited across the thin film pattern, there is a problem of disconnection.

In order to solve this problem, various methods have been proposed for making the side walls of the thin film pattern gently sloped, so-called tapered. However, these methods include a method of controlling the taper angle of the material to be etched by adjusting the etching amount of the mask material by adjusting the composition of the etching gas, and a method of increasing the etching speed by creating an impurity concentration gradient in the material to be etched. Methods that require a high degree of controllability or add complex processes, such as methods that utilize the effect, or methods that anisotropically etch the thin film formed to cover the steps on the sidewalls so that the thin film remains only on the sidewalls. There are many methods to do this, and these methods cannot necessarily be said to be highly reproducible or stable.

(Means for Solving the Problems) The present invention has been made by focusing on these problems, and uses CCl ₄ , CCl ₃ F, CCl ₂ F ₂ ,
Contains at least one of CClF ₃ and CF ₄ ,
The present invention is characterized in that a mixed gas containing at least one kind of hydrocarbon gas having carbon number of 8 or less is used, and the purpose is to easily and stably form the side wall surface into a tapered shape. The present invention will be explained in detail below.

FIG. 1 is an example of a sectional view of a plasma etching apparatus used in the present invention. In the figure, 1 is a reaction chamber, 2 is a sample electrode on which a sample is placed, which is one of the electrode plates installed parallel to each other in the reaction chamber, 3 is a counter electrode installed opposite the sample electrode 2, and 4 5 is a gas inlet pipe attached to the sample electrode 2 to introduce the reaction gas for etching between the sample electrode 2 and the counter electrode 3; 5 is a gas exhaust pipe attached to the reaction chamber 1 to exhaust the gas in the reaction chamber to the outside; 6; 7 is a material to be etched placed on the sample electrode 2, and 7 is a high frequency power source connected to the sample electrode 2 on one side and to the counter electrode 3 on the other side for generating a plasma of an etching reaction gas. Note that the distance between both electrodes 2 and 3 is generally 2 to 10 cm.

In order to etch the material to be etched 6 using the plasma etching apparatus configured as described above, a reaction gas is introduced into the reaction chamber 1 and exhausted from the gas exhaust pipe 5 using a vacuum pump.
A high frequency voltage of 400 V to 1 KV and 13.56 MHz is applied between the sample electrode 2 and the counter electrode 3 while maintaining a vacuum of 10 ^-3 to several Torr inside to generate plasma by high frequency glow discharge. The active chemical species present in this plasma react with the material to be etched 6 made of single-crystal silicon or polycrystalline silicon to generate volatile compounds, which are exhausted and removed from the etching chamber through the exhaust pipe 5. Etching then progresses.

(Example) The plasma etching method of the present invention will be explained in detail below with reference to Examples.

A material to be etched 6 is placed on the sample electrode 2 in the reaction chamber 1.
Place. FIG. 2 is a cross-sectional view showing the structure of the material to be etched 6, in which 8 is a resist film which is a mask material;
9 is the As-doped polycrystalline silicon film which is the main object of etching, 10 is the underlying silicon dioxide film,
11 is the underlying single crystal silicon. Next, the inside of the reaction chamber 1 is evacuated using a vacuum pump, and the gas introduction pipe 4 is
For example, CCl ₂ F ₂ as a reactive gas for etching from
Introduced 50SCCM of C ₂ H ₆ and 10SCCM of C 2 H 6, respectively.
The degree of vacuum in the reaction chamber was maintained at 0.18 Torr. 800W of high-frequency power is applied between both electrodes to generate plasma and perform etching.

FIG. 3 is a cross-sectional view of the material to be etched 6 when etched under the above conditions, and the sidewall surfaces of the resist film 8 and the As-doped polycrystalline silicon film 9 are gently sloped and rounded.
It has a unique shape. At this time, the etching rates of the resist film (AZ1370 manufactured by Shipley) 8 and the As-doped polycrystalline silicon film 9 were 360 and 1020 Å/min, respectively. The unique cross-sectional shape of the etched material 6 as shown in the figure cannot be seen in plasma etching using a single gas such as CCl ₂ F ₂ as the etching gas. Although the details of the reason why the side wall of the material to be etched 6 takes on a peculiar shape are unknown, by using a mixed gas of CCl ₂ F ₂ and C ₂ H ₆ as the etching gas, a plasma polymerization reaction occurs in parallel with the etching reaction. This is presumed to be due to the fact that plasma polymer 12 is deposited on the surfaces of resist film 8 and As-doped polycrystalline silicon film 9 as etching progresses.

FIG. 4 shows the cross-sectional shape of the As-doped polycrystalline silicon film 9 after the resist film 8 and polymer 12 have been removed by oxygen plasma treatment on the etched material 6 etched with the above-mentioned mixed gas.
The side wall of the As-doped polycrystalline silicon film 9 has a gentle taper shape. In the above example, this taper angle was about 60 degrees.

As an etching reaction gas as mentioned above.
It is clear that by using a gas mixture of CCl ₂ F ₂ and C ₂ H ₆ the side walls of the material to be etched can be shaped into a tapered shape. In addition, in the above example, the taper angle was approximately 60 degrees, but the taper angle can be controlled by changing the mixing ratio of CCl ₂ F ₂ and C ₂ H ₆ and the degree of vacuum to increase or decrease the production rate of plasma polymer. be done. The mixing ratio of the hydrocarbon gas to CCl ₂ F ₂ is preferably 5 to 50% by weight.

The above uses CCl ₂ F ₂ as the etching reaction gas.
This _is an example _in which _{a mixed} gas of
CF ₄ ) or CCl ₄ and other hydrocarbon gases having 8 or less carbon atoms (for example, CH ₄ , C ₂ H ₂ , C ₂ H ₄ ) can be used in the same manner.

For example, CCl ₂ F ₂ as a reaction gas for etching.
50 SCCM of CH 4 and 20 SCCM of CH ₄ were introduced into the reaction chamber, the degree of vacuum was maintained at 0.2 Torr, and high frequency power of 800 W was applied between the electrodes to etch the material to be etched. The material to be etched is the same as in the above example.
An As-doped polycrystalline silicon film was used. As after etching and oxygen plasma treatment
The cross-sectional shape of the doped polycrystalline silicon film was similar to that shown in FIGS. 3 and 4 above.

In the above embodiment, an As-doped polycrystalline silicon film was used as the material to be etched, but polycrystalline silicon films containing doping atoms such as P or B, polycrystalline silicon films containing no impurities, single crystal silicon, etc. can also be applied.

As explained above, the present invention uses a hydrocarbon gas containing at least one of CCl ₄ , CCl ₃ F, CCl ₂ F ₂ , CCLF ₃ and CF ₄ and having a carbon number of 8 or less as an etching reaction gas. A tapered side wall surface is formed on the material to be etched by etching the material using a plasma reaction using a mixed gas containing at least one of the following, and there is no increase in the number of steps. This plasma etching method is simple and has good reproducibility, and contributes to improving yields in semiconductor device manufacturing.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the plasma etching apparatus used in the present invention, Fig. 2 is a sectional view of the material to be etched before etching, Fig. 3 is a sectional view of the material to be etched after etching, and Fig. 4 is after etching. FIG. 3 is a cross-sectional view of the material to be etched after oxygen plasma treatment. DESCRIPTION OF SYMBOLS 1...Reaction chamber, 2...Sample electrode, 3...Counter electrode, 4...Gas introduction tube, 5...Gas exhaust tube, 6...
... Material to be etched, 7 ... High frequency power supply, 8 ... Resist film, 9 ... As-doped polycrystalline silicon film,
10...Silicon dioxide, 11...Single crystal silicon, 12...Plasma polymer.

Claims (1)

[Claims] 1. An etching chamber equipped with a sample electrode on which the sample to be etched is placed and a counter electrode facing the sample electrode is evacuated while flowing a reaction gas, and the etching chamber is maintained at a vacuum level within a certain range, and both of the above-mentioned etching chambers are In the method of etching the sample to be etched using gas plasma generated by applying a high frequency voltage to an electrode, the reaction gas may include CCl ₄ ,
A mixed gas containing at least one of CCl ₃ F, CCl ₂ F ₂ , CClF ₂ and CF ₄ and at least one hydrocarbon gas having a carbon number of 8 or less is used. Plasma etching method.